I have noticed that my four processors are always working after loading a project including virtual synths and/or effects. I mean, even if I'm doing nothing, watching TV, drinking coffee or reading my e-mail on my smartphone without playing the project, my PC is working hard... It's not the case if I load a MIDI-only sequence, which is supposed to be played by my hardware synth : only one processor is working a little bit.
 
Sometimes you even get a noise created by some plugins, while the song is not playing.
 
I think that this behaviour should be an option. If I want my DAW to be immediately ready to work, it is interesting, but if not, why does it happen? I think it's a waste of energy and money, it makes my PC works a lot without any reason, and its fans too...
 
I think that there should be a green button to say "if I don't hit play for x minutes the processors can relax a little bit"... Obviously in a live or hard working environment I would disable this option.

There are numerous posts about Windows power management being problematic and this just adds another layer for possible failure. SONAR is a host, so adheres to what plugins want to do, and never knows when someone will hit the space bar - it needs to always be ready to go. The best option to achieve this (even now) is simply shut off the audio engine... that should drop your performance module to zero even with a project loaded. Turn it back on when you want to roll again.
 
I very much fear a computer deciding things for me.
 
Quick Edit: I just learned something new... if you shut off the audio engine manually and hit space bar, SONAR brings itself back online and starts playing! (My "Dayum, that was cool" moment for the day )

Sonar is rather smart is decision either call some plug-in or not. But,
a) if there is a route from echo enabled audio input or there is a possibility some plug-in is a "generator", the whole chain should continue to work
b) you jamming/recording for a while and.... BUM, your computer went to sleep. Yes, you can unset that in Windows. But you forgot. You want yet another such option to be forgotten build into Sonar? Sonar tries to avoid that on purpose, see "Quick Edit" in the previous post

Thank you for the replies, I didn't know that the audio engine shut off could be used in this way (I thought it was more in case of problems happening sometimes). That's a good idea, that fits my needs!